Concern for the healthy development of the fetus and the premature infant continues to spawn considerable interest in prenatal behavior, yet relatively little is known about how a fetus behaves and responds to changes within its uterine environment. In spite of technological advances, methodological problems and ethical considerations have limited the study of the human fetus to indirect monitoring and postnatal inference. Therefore, direct observation and experimentation is possible only with nonhuman subjects. Recent technical developments now enable precise manipulation of the intrauterine environment of the rat fetus and observation of fetal behavior in utero. With the pregnant female rat surgically prepared by reversible spinal anesthesia or more long-lasting chemomyelotomy, her uterus may be externalized into a warm saline bath and the intrauterine environment manipulated by intra-amniotic injection, chemosensory stimulation delivered by intraoral infusion, and behavior of the fetus directly observed through the uterine wall (in utero) or within an unrestrained fluid medium (ex utero). These procedural tools now permit study of the developing mammalian fetus in its environment. This proposal outlines a general program of research to investigate the behavioral biology of the rat fetus. The objective of the proposed research is fivefold: (a) to develop and improve methodologies for the study of fetal behavior, (b) to identify age-related and environmental influences on the emergence and organization of spontaneous fetal behavior, (c) to manipulate the prenatal chemical milieu to map the sensory and learning abilities of the fetus, (d) to examine the transition from prenatal to postnatal life in an effort to identify behavioral continuities, and (e) to investigate the ability of the fetus to respond to suboptimal intrauterine conditions and estimate their long- term consequences.